During the transfer of a volatile liquid such as gasoline or a similar fuel, from a storage facility to a tank, there is normally an unsealed connection made between the disconnectable nozzle and the tank being filled. As the fuel transfer operation progresses, residual fuel vapor air mixture displaced from the tank normally passes into the atmosphere.
Many municipalities and governmental agencies have proposed or adopted regulations to reduce these emissions. One method toward complying with mandated regulations is the provision of a completely closed or balanced system between the fuel source and the tank being filled.
In the instance of a closed system, the latter normally includes a conduit which carries fuel, the remote end of which is communicated with a manually operated dispensing nozzle. The nozzle is adapted to be removably positioned within the filler pipe of a receiving tank. It further includes means to form a sealed engagement between the dispensing nozzle and the tank filler tube.
In the instance of a closed or balanced system, the storage facility tank is usually vented to the atmosphere. With such an arrangement as the liquid fuel is pumped, one of two events could occur. If fuel volume leaving the system is not immediately replaced by a vapor volume from the tank being filled, air will be drawing into the system. On the other hand, when a vapor volume in excess of the fuel volume comes from the tank being filled, some of the vapor will be vented. However, these exiting vapors must first be processed such that their discharge is not harmful to the environment.
Several embodiments of sealing arrangement have been found to be advantageous for providing the necessary vapor tight disconnectable connection in the nozzle spout. One method for providing the desired seal is to attach a substantially cylindrical flexible walled member such as a rubber boot or the like to the fuel dispensing nozzle. The boot, at the tank neck contact end, is equipped with a face seal containing a resilient contact surface.
By use of such an arrangement, when the nozzle is registered in the filler pipe of a receiving tank, the walls of the flexible boot will be deflected or distorted. The boot will therefore define an annular vapor passage while a resilient contact face sealably engages the tank filler pipe.
This type of arrangement has generally been found to be effective. Thus, when a fuel flow is introduced from the dispensing nozzle into the receiving tank, a slight pressure is produced within the latter to displace fuel vapor-air mixture. This displaced mixture will be urged through the passage defined by the nozzle spout and the flexible walled boot. Said mixture is then transferred by way of the dispensing nozzle through a separate conduit, to the fuel source.
The effectiveness of a balanced system depends to a large extent on the mechanical compatibility of the vehicle with the dispensing nozzle to permit a tight seal at the interface thereof. If for any reason the contact edges of the nozzle cannot engage the filler pipe, a seal cannot be readily achieved and a leak will result or subsequently develop. In addition if the resilient sealing face and rubber boot are not adequately maintained, leaks will result at those points.
Another potential source of vapor leakage is through the above tank venting means. Such tanks are normally present on vehicles, particularly those manufactured prior to 1971. When a leakage path does develop or exist at least some of the vapor that would normally enter the receiving tank, will enter into the atmosphere. Thus, in conjunction with closed or balanced fuel systems, vacuum assist means such as jet pumps, fans, blowers, etc. have been devised which cause the vapor collection system to operate under a slight vacuum. This condition tends to draw air into the fuel system through any leak paths which exist or develop. It further tends to inhibit the flow of vapor into the atmosphere.
Vacuum assist facilities, however, often embody the disadvantage of bringing in excessive amounts of air which could produce an undesired explosive mixture within the vapor space. Further, they could produce excessive vent pipe emissions due to the saturation of the excess air as it passes through the system in contact with gasoline. In addition they could place heavy burdens on any vapor removal facilities downstream of the storage facility.
Of further note, the temperature of fuel held within the storage tank and the temperature of the fuel held within the tank being filled for the most part will determine the volume of vapor flow experienced during a filling operation. For example, at a temperature differential, very cool dispensed fuel flowing into a warm partly filled tank can occur, such that little vapor will flow from the tank being filled. It has been found, however, that the temperature differential, during most filling operations falls within a limited range, resulting in vapor/liquid volume ratios of unity or slightly less.
In the presently disclosed arrangement, a system is provided which incorporates features which include (1) a tight seal at the vehicle nozzle interface for those vehicles which permit it; (2) a presure sensing device which will sense if the desired vacuum is available; (3) liquid chilling means to transfer heat from a fuel flow as the latter enters a receiving tank if a desired vacuum level is not available; (4) pressure/vacuum vent on the storage facility to maintain a desired pressure (vacuum) range in the storage facility and (5) provision to prevent air to leak through the nozzle between filling operations.
Toward assuring operation of the overall system under varying circumstances, a heat transfer system is included in the liquid fuel conduit or line. This system responds to pressure (vacuum) in the storage facility to reduce the temperature of the fuel dispensed and therefore reduce the vapor/liquid ratio to maintain or produce a vacuum in the storage tank.
An object of the invention, therefore, is to provide a fuel system which is adapted to minimize the passage of fuel vapors to the atmosphere. A further object is to provide a system which will maintain a vacuum at the nozzle tank filler neck interface. A still further object is to provide a system adapted to automatically obtain a desired vapor/liquid ratio during fuel pumping operations where a satisfactory vacuum is not maintained.